This research has three objectives. The first is to study the origin of chromosome replication in E. coli and to investigate the mechanism of initiation at this site. The second objective is to study the mode of DNA replication used by bacteriophage mu and to investigate its integration and excision. The third objective is to study the mechanism by which the Salmonella phage epsilon 15 infects its host cell with emphasis on how and where DNA is released and how it crosses the cell membrane.